Do not block on allocating buffers

There is really no point in doing that because this can be done
in an async way such that the first and subsequent dequeueBuffer
still don't block because at that point allocation is very likely
done.

Furthermore, avoid calling setAsyncMode initially, as it will also
block RT on buffer allocation. However, the default is false in
any case, so we really don't need to call it.

Also, only allocate one buffer at a time and don't block in
dequeueBuffer on allocating buffers. It will likely have one buffer
available already, and there is no point in waiting for other
buffers to be allocated.

Test: Press home with memory contention, observe less delay.
Test: General smoke testing for increased jank
Bug: 111517695
Change-Id: I9deb435013b2503178d2fe032151c1aaedd667af